Fluidized bed furnace

ABSTRACT

Provided is a fluidized bed furnace for heating waste to extract a combustible gas from the waste, including: a plurality of wind boxes arranged on a lower side of a bottom wall of a furnace body to blow a fluidizing gas into the fluidized bed; a plurality of temperature detection sections disposed at respective positions allowing detection of temperatures of an upper position and a lower position vertically spaced in a first region, and allowing detection of temperatures of upper and lower positions vertically spaced in a second region; and a control section operable, based on the temperatures detected by the temperature detection sections, to adjust an air ratio of the fluidizing gas to be fed to each of the wind boxes, so that the temperature of the fluidized bed is raised in a direction from the first region toward the second region.

TECHNICAL FIELD

The present invention relates to a fluidized bed furnace designed toheat waste in a fluidized bed formed by fluidizing fluidizable particlesto thereby extract a combustible gas from the waste.

BACKGROUND ART

Heretofore, there has been known a fluidized bed furnace described inthe following Patent Document 1. As illustrated in FIG. 5, thisfluidized bed furnace comprises a furnace body 104 having fluidizablesand (fluidizable particles) 102 in a furnace bottom section, and an airsupply section 106 for supplying air into the fluidizable sand 102 inthe furnace bottom section so as to fluidize the fluidizable sand 102 toform a fluidized bed. The furnace body 104 has a sidewall. The sidewallis provided with an input section 108 for inputting waste onto thefluidized bed therefrom.

In this fluidized bed furnace 100, the air supply section 106 is adaptedto supply air into high-temperature fluidizable sand 102 to therebyfluidize the fluidizable sand 102 in a fluidizing state. Consequently, afluidized bed is formed in fluidized bed furnace 100. The air supplysection 106 is operable to supply air in such a manner that a fluidizedstate of the fluidizable sand 102 becomes approximately equalized in theentire region of the fluidized bed so as to allow waste input from theinput section 108 onto the fluidized bed to be entrapped inside thefluidized bed and efficiently combusted.

Every time waste is input from the input section 108 onto thehigh-temperature fluidizable sand 102, the input waste is mixed with thehigh-temperature fluidizable sand 102 of the fluidized bed, andthermally decomposed (gasified). Consequently, a combustible gas isgenerated. For example, this combustible gas will be combusted at hightemperatures in a melting furnace in a subsequent stage.

Waste input into the fluidized bed furnace 100 is entrapped in theactive fluidized bed and combusted or gasified. In this process, everytime waste is intermittently input, combustible substances in the wasteare rapidly combusted, so that a rapid fluctuation in amount,concentration, etc., of a generated combustible gas will repeatedlyoccur. A change in the gasification reaction is largely dependent on aquantitative characteristic in supply of waste. Thus, in the case wherethere is a fluctuation in supply of waste or a qualitative change incomponents of waste, it is impossible to stably generate a combustiblegas. Particularly, when a large amount of easily combustible trash suchas paper or sheet-shaped plastic is comprised in waste, a fluctuation ofgeneration of a combustible gas becomes larger, and therefore there is aneed for stabilizing the gas generation.

For example, in the case where generated combustible gas is used for agas engine to generate electric power, if a combustible gas is generatedwith large fluctuations, it is impossible to obtain stable energy.Therefore, there is a need for further stabilizing a combustible gas tobe obtained in a fluidized bed furnace.

LIST OF PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP 2006-242454A

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a fluidized bedfurnace capable of stably obtaining a combustible gas even from wastecomprising easily combustible trash.

The fluidized bed furnace according to the present invention is designedto heat waste to extract a combustible gas from the waste. The fluidizedbed furnace comprises: a furnace body having a bottom wall whichsupports fluidizable particles from therebelow so as to make up afluidized bed for heating the waste, and a sidewall standing upwardlyfrom the bottom wall, wherein the bottom wall has a discharge portprovided at a position offset from a center position of the bottom wallin a specific direction to discharge non-combustible substances in thewaste together with a part of the fluidizable particles, and an uppersurface of the bottom wall is inclined to become lower toward thedischarge port so as to cause the non-combustible substances to fall onthe upper surface of the bottom wall toward the discharge port; a gassupply section for blowing a fluidizing gas from the bottom wall of thefurnace body toward the fluidizable particles to fluidize thefluidizable particles; a plurality of temperature detection sections fordetecting a temperature of the fluidized bed; a control section forcontrolling the gas supply section; and a waste supply section forsupplying waste from a supply-side portion of the sidewall located on aside opposite to the discharge port across the center position of thebottom wall, to a region on the fluidized bed, the region being adjacentto the supply-side sidewall portion. The gas supply section includes aplurality of wind boxes each of which is provided on a lower side of thebottom wall to extend in a direction orthogonal to a direction from thesupply-side sidewall portion toward the discharge port and adapted toblow the fluidizing gas from a given position in the orthogonaldirection toward the fluidizable particles, and a feeding unit adaptedto feed the fluidizing gas to each of the wind boxes in a manner capableof adjusting an air ratio of the fluidizing gas to be fed to each of thewind boxes, individually. The plurality of wind boxes are arrangedside-by-side in the direction from the supply-side sidewall portiontoward the discharge port. The plurality of temperature detectionsections are disposed at respective positions allowing detection oftemperatures of an upper position and a lower position which arevertically spaced in a first region of the fluidized bed, the firstregion vertically overlapping with a first one of the wind boxes closestto the supply-side sidewall portion, and allowing detection oftemperatures of an upper position and a lower position which arevertically spaced in a second region of the fluidized bed, the secondregion vertically overlapping with the discharge port or a second one ofthe wind boxes closest to the discharge port. The control section isoperable, based on the temperatures detected by the temperaturedetection sections, to adjust an air ratio of the fluidizing gas to befed from the feeding unit to each of the wind boxes, individually, insuch a manner that the temperature of the fluidized bed is raised in adirection from the first region toward the second region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a fluidized bed furnaceaccording to one embodiment of the present invention.

FIG. 2 is a horizontal sectional view taken along the line II-II in FIG.1.

FIG. 3 is a diagram for explaining upward regions and an arrangement oftemperature sensors, in a fluidized bed of the fluidized bed furnace.

FIG. 4 is a diagram for explaining an arrangement of temperature sensorsin a fluidized bed furnace according to another embodiment of thepresent invention.

FIG. 5 is a schematic configuration diagram of a conventional fluidizedbed furnace.

DESCRIPTION OF EMBODIMENTS

With reference to the accompanying drawings, the present invention willnow be described based on one embodiment thereof.

A fluidized bed furnace (fluid bed furnace) according to this embodimentis designed to heat waste by high-temperature fluidizable particles(fluidizable sand), to extract a combustible gas from the waste. Forexample, waste as a target substance to be treated by the fluidized bedfurnace includes wood-based biomasses (pruned branch, lumber, etc.) andcombustible substances (plastic, fluff, paper, etc.), and mixturethereof.

As illustrated in FIGS. 1 and 2, the fluidized bed furnace comprises: afurnace body 20 internally having fluidizable particles 12 making up afluidized bed 14; a gas supply section 30 for supplying a fluidizing gasto an inside of the furnace body 20, a plurality of temperature sensors(temperature detection sections) 40 for detecting a temperature of thefluidized bed 14, a control section 50 for controlling the gas supplysection 30, and a waste supply section 60 for supplying waste 18 intothe furnace body 20.

The fluidizable particles 12 make up the fluidized bed 14 to heat waste18, inside the furnace body 20. More specifically, the fluidizableparticles 12 heated up to a high temperature by combustion of a part ofpreviously supplied waste 18 are mixed with new waste 18, so that thenew waste 18 is gasified to generate a combustible gas. For example, thefluidizable particles 12 may be silica sand.

The furnace body 20 is designed to extract a combustible gas from waste18 by means of the high-temperature fluidizing particles 12. The furnacebody 20 has a bottom wall 21 supporting the fluidizable particles 12from therebelow, a sidewall 22 standing upwardly from the bottom wall21, and a combustible gas outlet portion 23 provided at an upper end ofthe sidewall 22.

The sidewall 22 has a rectangular tubular shape extending in an up-down(vertical) direction. Specifically, the sidewall 22 has a front wall(supply-side sidewall portion) 24 and a rear wall 25 which are disposedin opposed and spaced-apart relation to each other in a front-reardirection (in FIG. 2, in a right-left direction), and a pair of lateralwalls 26, 26 each connecting corresponding ends of the front wall 24 andthe rear wall 25. The lateral walls 26, 26 are disposed parallel to eachother. In other words, the furnace body 20 has a shape in plan view, inwhich a dimension in a width direction (widthwise dimension) as adistance between the lateral walls 26, 26 is equalized in the front-reardirection.

A portion (front wall) 24 of the sidewall 22 located on a side oppositeto an aftermentioned discharge port 29 across a center position of thebottom wall 21 has a waste introduction port 28 for introducing waste 18into the furnace body 20. In this embodiment, as illustrated in FIG. 2,the term “front-rear direction” means a front-rear direction of thefurnace body 20 (in FIG. 2, a right-left direction), and the term “widthdirection” means a width direction of the furnace body 20 (in FIG. 2, anup-down direction).

The waste introduction port 28 is provided in a central region of alower portion of the front wall 24 in the width direction. The wasteintroduction port 28 is provided at a height position where waste 18 canbe pushed generally horizontally onto an upper surface of thefluidizable particles 12 (fluidized bed 14) supported by the bottom wall21 of the furnace body 20. More specifically, the waste introductionport 28 is provided in such a manner that a lower end thereof is locatedat a position slightly above the upper surface of the fluidized bed 14.

The combustible gas outlet portion 23 is designed to dischargecombustible gas generated inside the furnace body 20. The combustiblegas outlet portion 23 has an outer diameter squeezed more than thesidewall 22, so that a duct or the like for supplying the combustiblegas obtained in the furnace body 20 to a subsequent stage, for example,a gas engine for electric power generation processes, can be connectedthereto.

The bottom wall 21 has a discharge port 29 provided at a position offsetfrom the center position thereof in a specific direction to dischargenon-combustible substances in waste 18 together with a part of thefluidizable particles 12. The discharge port 29 has an opening locatedin a widthwise central region of the bottom wall 21 at the offsetposition. The bottom wall 21 has an upper surface 21 a inclined tobecome lower toward the discharge port 29. This allows non-combustiblesubstances and others to fall on the upper surface 21 a. In thisembodiment, the upper surface 21 a of the bottom wall 21 is divided intoa region 211 on a front side (in FIG. 2, left side) of the dischargeport 29, a region 212 on a rear side (in FIG. 2, right side) of thedischarge port 29, and two regions 213, 214 on widthwise both sides ofthe discharge port 29. Each of the regions 211, 212, 213, 214 is aninclined surface having a constant downward slope toward the dischargeport 29. In other words, the discharge port 29 is provided in the uppersurface 21 a of the bottom wall 21 at its downmost position.

The gas supply section 30 is designed to blow a fluidizing gas from thebottom wall 21 toward the fluidizable particles 12 to fluidize thefluidizable particles 12. The gas supply section 30 comprises aplurality of nozzles 31 installed to the bottom wall 21, a plurality ofwind boxes 32 for distributing the fluidizing gas to the respectivenozzles 31, and a feeding unit 33 for feeding the fluidizing gas to eachof the wind boxes 32. In this embodiment, in the bottom wall 21, two ormore of the plurality of nozzles 31 are arranged in a row in the widthdirection, and a plurality of the widthwise rows of nozzles 31 arearranged side-by-side in the front-rear direction. In other words, theplurality of nozzles 31 are installed to the bottom wall 21 inspaced-apart relation to each other in the width direction and thefront-rear direction, i.e., in a lattice arrangement. Each of thenozzles 31 is attached to the bottom wall 21 to penetrate through thebottom wall 21. It is to be understood that a layout of the nozzles 31is not limited to the lattice arrangement.

Each of the wind boxes 32 is designed to allow the fluidizing gas to beblown from given widthwise positions of the bottom wall 21 to the insideof the furnace body 20 via one or more of the rows of nozzles 31. Thewind box 32 has a box shape capable of being installed on a lower sideof the bottom wall 21 in such a manner as to extend in the widthdirection. The wind box 32 serves as a header for distributing thefluidizing gas to the corresponding one or more rows of nozzles 31arranged in the width direction in the bottom wall 21. In other words,the wind box 32 has a function of equalizing respective flow rates ofthe fluidizing gas to be blown from the corresponding one or more rowsof nozzles 31 arranged in the width direction. In this embodiment, acommon fluidizing gas is distributed from each of the wind boxes 32 totwo of the rows of nozzles 31 located adjacent to each other in thefront-rear direction.

The plurality of wind boxes 32 are provided on the side of a lowersurface of the bottom wall 21 and arranged side-by-side in thefront-rear direction. Thus, with respect to each group of the two rowsof nozzles 31 corresponding to a respective one of the wind boxes 32, acomposition and/or a flow rate of the fluidizing gas to be blown fromthe two rows of nozzles 31 can be changed. In this embodiment, threewind boxes 32 a, 32 b, 32 c are arranged side-by-side in the front-reardirection. Specifically, two wind boxes (a first wind box 32 a and asecond wind box 32 b) are disposed on the side of the front wall 24 withrespect to the discharge port 29, and one wind box (a third wind box 32c) is disposed on the side of the rear wall 25 with respect to thedischarge port 29.

The feeding unit 33 comprises an air feeder 34 for feeding air (oxygen),a steam feeder 35 for feeding steam, and a plurality of pipe lined 36connecting each of the feeders 34, 35 to the wind boxes 32. The feedingunit 33 is adapted to feed air and steam from respective ones of thefeeders 34, 35 to the wind boxes 32 via the pipe lines 36, individually.In this embodiment, the fluidizing gas is composed of air and/or steamfed from the air feeder 34 and/or the steam feeder 35 to each of thewind boxes 32.

Each of the pipe lines 36 is provided with a respective one of aplurality of valves 37 a, 37 b, 37 c, 38 a, 38 b, 38 c to adjust a flowrate of fluid (in this embodiment, air or steam) flowing through thepipe line 36. Each of the valves 37 a, 37 b, 37 c, 38 a, 38 b, 38 c isadapted to change a degree of valve opening, according to a controlsignal from the control section 50. This allows adjustment of anair/fuel ratio (oxygen concentration) of the fluidizing gas to besupplied from the wind boxes 32 into the inside of the furnace body 20.

Each of the plurality of temperature sensors 40 is designed to detect atemperature of the fluidized bed 14. The plurality of temperaturesensors 40 are provided inside the furnace body 20. Each of thetemperature sensors 40 is connected to the control section 50 andoperable to convert a detected temperature to a temperature signal andinput the temperature signal into the control section 50.

The temperature sensors 40 are allocated in a plurality of regions ua₁,ua₂, ua₃ of the fluidized bed vertically overlapping with respectiveones of the wind boxes 32 (each of the regions will hereinafter bereferred to as “upside region”). Specifically, the temperature sensors40 are arranged to allow detection of temperatures of an upper positionand a lower position which are vertically spaced in each of the upsideregions ua₁, ua₂, ua₃. In this embodiment, a total number six oftemperature sensors 40 are provided. More specifically, three sets oftwo temperature sensors 40 are allocated, respectively, in the upsideregion (first region) ua₁ of the first wind box 32 a, the upside region(third region) ua₃ of the second wind box 32 b, and the upside region(second region) ua₂ of the third wind box 32 c. In this embodiment, thethree wind boxes 32 are provided in the furnace body 20, and thereforethe number of the upside regions ua₁, ua₂, ua₃ is three. It is to beunderstood that when the number of the wind boxes 32 is increased, thenumber of the upside regions is increased in proportion thereto.Further, the term “upper position” means a position above a center ofthe fluidized bed 14 in the vertical direction. The term “lowerposition” means a position below the center of the fluidized bed 14. Inthis regard, however, the upper position is located at a given depth ormore so as to become insusceptible to a gas temperature and a wastetemperature above the upper surface of the fluidized bed 14. The lowerposition is located above the upper surface 21 a of the bottom wall 21by a given distance or more so as to become insusceptible to atemperature of the bottom wall 21 itself.

The two temperature sensors 40 allocated in each of the upside regionsua₁, ua₂, ua₃ are not necessarily arranged at vertically overlappingpositions, as long as they can detect respective temperatures of theupper position and the lower position in the upside region (ua₁, ua₂,ua₃). In other words, one of the two temperature sensors 40 fordetecting the temperature of the upper position and the othertemperature sensor 40 for detecting the temperature of the lowerposition may be arranges at respective positions offset in the widthdirection in the upside region (ua₁, ua₂, ua₃) (see FIG. 2).Alternatively or additionally, the one temperature sensor 40 fordetecting the temperature of the upper position and the othertemperature sensor 40 for detecting the temperature of the lowerposition may be arranged at respective positions offset in thefront-rear direction in the upside region (ua₁, ua₂, ua₃) (morespecifically, in a region between a blowout port row of a front one ofthe two rows of nozzles 31 and a blowout port row of a rear one of thetwo rows of nozzles 31 (see each shaded area in FIG. 3)).

As long as the temperature sensors 40 are arranged to allow thetemperatures of the upper position and the lower position to be detectedin each of the first region ua₁ and the second region ua₂, the number ofthe temperature sensors 40 in each of the remaining one or more upsideregions (in this embodiment, the third region ua₃) may be one.Alternatively, the number of the temperature sensors 40 to be allocatedin each of the upside regions ua₁, ua₂, ua₃ may be three or more.

It is to be understood that, as long as the temperature sensors 40 arearranged to allow the temperatures of the upper position and the lowerposition to be detected at least in each of the first region ua₁ and thesecond region ua₂, a total number and an arrangement of the temperaturesensors 40 to be provided inside the furnace body 20 are not limited toa specific number or specific positions.

For example, the number of the temperature sensors 40 to be allocatedbetween the first region ua₁ and the second region ua₂ may be one. Inanother example, specific ones of the plurality of temperature sensors40 may be arranged at respective positions allowing detection oftemperatures at given intervals in the front-rear direction (e.g.,arranged in the front-rear direction in a row when viewed in the widthdirection (see FIG. 4)). In this case, the specific temperature sensors40 may be arranged in each of one or more upside regions (in thisembodiment, the third region ua₃) located between the first region ua₁and the second region ua₂, or may be arranged at given intervals in thefront-rear direction, irrespective of the upside regions ua₁, ua₂, ua₃.This arrangement makes it possible to detect temperatures between thefirst region ua₁ and the second region ua₂ in the fluidized bed 14,thereby detecting local temperature abnormality of the fluidized bed 14,e.g., a local lowering in temperature between the first region ua₁ andthe second region ua₂.

Preferably, the specific temperature sensors 40 are arranged atrespective positions additionally allowing detection of temperatures ofan upper position and a lower position in each of the one or more upsideregions (ua₃) between the first region ua₁ and the second region ua₂.Based on arranging the specific temperature sensors 40 in this manner,it becomes possible to desirably detect defective fluidization in theone or more upside regions (ua₃) between the first region ua₁ and thesecond region ua₂ of the fluidized bed 14. Specifically, in a situationwhere, when the fluidizing gas is supplied from the bottom wall 21 intothe fluidized bed 14, the fluidizable particles 12 in a region suppliedwith the fluidizing gas is in a sufficiently fluidized state, thesupplied fluidizing gas will easily move upwardly through the fluidizedbed 14. However, if defective fluidization occurs in the region ua, thefluidizing gas becomes hard to move upwardly through the fluidized bed14. Thus, in and around the region having the defective fluidization,the fluidizable particles 12 are not sufficiently agitated. This causesa temperature difference between an upper position and a lower positionin this region, so that this temperature difference is detected todetect the defective fluidization in this region.

The control section 50 is operable, based on the temperatures detectedby the temperature sensors 40, to adjust an air ratio of the fluidizinggas to be fed from the feeding unit 33 to each of the wind boxes 32,individually. More specifically, the control section 50 is operable toadjust an air ratio of the fluidizing gas to be fed to each of the windboxes 32 by controlling the feeding unit 33 in such a manner that atemperature of the fluidized bed 14 is raised toward a rear side (i.e.,in a direction from the front wall 24 toward the rear wall 25). Thismakes it possible to suppress a rapid fluctuation in amount,concentration, etc., of a combustible gas to be generated in thefluidized furnace 10. As a result, the fluidized furnace 10 can stablygenerate a combustible gas from waste 18.

The control section 50 is also operable, based on the temperaturesdetected by the temperature sensors 40, to detect fluidizationabnormality (local defective fluidization, etc.) and control a gasfeeding section 30 to an air ratio and/or a flow rate of the fluidizinggas to be supplied to the inside of the furnace body 20. This makes itpossible to solve the fluidization abnormality.

Specifically, the control section 50 is configured to control respectivetemperatures of the regions of the fluidized bed 14 in the front-reardirection in the following manner (first method). In this embodiment,assume that the three sensors 40 on an upper side in FIG. 1 are definedas a first sensor, a second sensor and a third sensor in order from theleft side, and the three sensors 40 on a lower side in FIG. 1 aredefined as a fourth sensor, a fifth sensor and a sixth sensor in orderfrom the left side, wherein a temperature detected by the first sensor,a temperature detected by the second sensor, a temperature detected bythe third sensor, a temperature detected by the fourth sensor, atemperature detected by the fifth sensor and a temperature detected bythe sixth sensor are represented as T₁, T₂, T₃, T₄, T₅ and T₆,respectively.

In response to receiving temperature signals from the temperaturesensors 40, the control section 50 acquires temperatures in each of theregions (regions in which the temperature sensors 40 are allocated) ofthe fluidized bed 14, and calculates an average value Ave1 of T₁ and T₄,an average value Ave2 of T₂ and T₅ and an average value Ave3 of T₃ andT₆. Then, the control section 50 compares the averages Ave1, Ave2 andAve3.

When the relation “Ave1<Ave2<Ave3” is broken, the control section 50instructs the feeding unit 33 to temporarily increase a flow rate of thefluidizing gas to be supplied to each of the wind boxes 32. In thisregard, although the control section 50 in this embodiment is configuredto continually monitor the relation “Ave1<Ave2<Ave3”, it may beconfigured to monitor the relation “Ave1<Ave2<Ave3” at intervals of agiven time.

More specifically, when the control section 50 detects temperatureabnormality in response to a change to “Ave1>Ave2” or “Ave2>Ave3”, itoperates to increase the flow rate of the fluidizing gas to be fed tothe wind boxes 32. During this process, the control section 50 operatesto increase only the flow rate of the fluidizing gas to be blown fromeach of the wind boxes 32 to the inside of the furnace body 20, whilekeeping a ratio between air and vapor to be fed to each of the windboxes 32 (i.e., air ratio of the fluidizing gas) at a constant value.Specifically, upon detection of the temperature abnormality, the controlsection 50 operates to temporarily increase the flow rate of thefluidizing gas to be blown from each of the wind boxes 32 into thefluidized bed 14, from a normal flow rate (e.g., Uo/Umf=3.0) (forexample, an increased flow rate Uo/Umf=5.0). In the above description,Umf is a minimum fluidization velocity which is a minimum flow velocityof the fluidizing gas to be blown so as to fluidize the fluidizableparticles 12, and Uo is a cross-sectional average flow velocity of thefluidizing gas.

Then, when temperatures detected by the temperature sensors 40 satisfythe relation “Ave1<Ave2<Ave3”, the control section 50 controls thefeeding unit 33 to return the flow rate of the fluidizing gas to beblown from each of the wind boxes 32 into the fluidized bed 14, to anoriginal value (in the above example, return the Uo/Umf from 5.0 to3.0), and continues the temperature monitoring. On the other hand, in asituation where the temperatures detected by the temperature sensors 40do not satisfy the relation “Ave1<Ave2<Ave3” even when a certain timehas elapsed after starting to increase the flow rate of the fluidizinggas, the control section 50 determines that abnormality occurs in theinside of the furnace body 20. Then, the control section 50 stops anoperation of the fluidized bed furnace 10.

More specifically, for example, in a normal operation state of thefluidized bed furnace 10 where no temperature abnormality occurs in thefluidized bed 14, Ave1, Ave2 and Ave3 are about 600° C., about 650° C.and about 700° C., respectively. Assume that this Ave1 is increased to660° C. due to a change in amount and/or composition of waste 18supplied to the inside of the furnace body 20. In this situation, inresponse to detection of temperature abnormality (Ave1>Ave2), thecontrol section 50 operates to temporarily increase the flow rate of theflow rate of the fluidizing gas to be blown from each of the wind boxes32 into the fluidized bed 14. Thus, while the Ave1, the Ave2 and theAve3 are increased, respectively, to 700° C., 750° C. and 800° C., andthe temperature of the fluidized bed 14 is raised in its entirety, thelocal defective fluidization, etc., of the fluidized bed 14, is solved,and a temperature balance of the inside of the furnace is recovered.Consequently, the temperatures detected by the temperature sensors 40start satisfying the relation “Ave1<Ave2<Ave3”. Subsequently, when thecontrol section 50 operates to return the flow rate of the fluidizinggas to be blown from each of the wind boxes 32 into the fluidized bed14, to the original value, the Ave1, the Ave2 and the Ave3 are returnedto about 600° C., about 650° C. and about 700° C., respectively, and thetemperature abnormality occurring in the fluidized bed is solved.

In this method, the control section 50 may be configured to, in asituation where, although the temperatures detected by the temperaturesensors 40 satisfy the relation “Ave1<Ave2<Ave3”, Ave1 and Ave3 aredeviated, respectively, from their given ranges (min₁<Ave1<max₁ andmin₃<Ave3<max₃), temporarily increase the flow rate of the fluidizinggas to be blown from each of the wind boxes 32 into the fluidized bed14. Thus, the control section 50 can more desirably maintain atemperature distribution of the fluidized bed in the front-reardirection (i.e., a temperature distribution in which the temperature ofthe fluidized bed 14 is gradually raised in the direction from the frontwall 24 toward the rear wall 25).

Alternatively, the control section 50 may be configured to controlrespective temperatures of the regions of the fluidized bed 14 in thefront-rear direction in the following manner (second method).

The control section 50 operates to monitor the relation“Ave1<Ave2<Ave3”, in the same manner as that in the aforementionedmethod. Specifically, in response to receiving temperature signals fromthe temperature sensors 40, the control section 50 acquires temperaturesin each of the regions of the fluidized bed 14 and calculates averagevalues Ave1, Ave2, Ave3 thereof. Then, the control section 50 comparesthe averages Ave1, Ave2 and Ave3. In this method, the control section 50may be configured to continually monitor the relation “Ave1<Ave2<Ave3”,or may be configured to monitor the relation “Ave1<Ave2<Ave3” atintervals of a given time.

When the relation “Ave1<Ave2<Ave3” is broken, the control section 50instructs the feeding unit 33 to adjust a ratio between air and vapor tobe fed to one of the wind boxes 32 corresponding to an abnormal one ofthe regions. For example, when high-temperature abnormality occurs inthe first region ua₁ to cause the relation “Ave1>Ave2”, the controlsection 50 controls the feeding unit 33 to close the valve 37 a toreduce a flow rate of air to be fed to the first wind box 32 and openthe valve 38 a to increase a flow rate of steam to be fed to the firstwind box 32, while keeping a flow rate of the fluidizing gas to be blownfrom the first wind box 32 into the fluidized bed 14. Thus, an air ratioof the fluidizing gas to be blown from the first wind box 32 into thefluidized bed 14 becomes smaller. In other words, an oxygenconcentration is lowered. Subsequently, the control section 50 continuesthe temperature monitoring, and, when the relation “Ave1<Ave2” issatisfies, operates to return the valves 37 a, 38 a, respectively, totheir original positions (i.e., open the valve 37 a and close the valve38 a) to return the air ratio (oxygen concentration) of the fluidizinggas to be blown from the first wind box 32 into the fluidized bed 14, toan original value. On the other hand, in a situation where thetemperatures still have the relation “Ave1>Ave2” even when a given timehas elapsed after starting to reduce the air ratio of the fluidizing gasto be blown from the first wind box 32 into the fluidized bed 14, thecontrol section 50 determines that abnormality occurs in the inside ofthe furnace body 20, and stops the operation of the fluidized bedfurnace 10.

In this method, the control section 50 may be configured to, to in asituation where, although the temperatures detected by the temperaturesensors 40 satisfy the relation “Ave1<Ave2<Ave3”, Ave1 and Ave3 aredeviated, respectively, from their given ranges (min₁<Ave1<max₁ andmin₃<Ave3<max₃), adjust respective valve openings of the valves 37 a, 37c, 38 a, 38 c (i.e., adjust an air ratio of the fluidizing gas to beblown from the first wind box 32 a into the fluidized bed 14 and an airratio of the fluidizing gas to be blown from the third wind box 32 cinto the fluidized bed 14) to return the Ave1 and the Ave3,respectively, to the given ranges. Specifically, when low-temperatureabnormality occurs in the first region ua₁ of the fluidized bed 14, thecontrol section 50 controls the feeding unit 33 to open the valve 37 aand close the valve 38 a to increase the air ratio of the fluidizing gasto be blown from the first wind box 32 a into the fluidized bed 14,while keeping the flow rate of this fluidizing gas. On the other hand,when high-temperature abnormality occurs in the second region ua₂ of thefluidized bed 14, the control section 50 controls the feeding unit 33 toclose the valve 37 c and open the valve 38 c to reduce the air ratio ofthe fluidizing gas to be blown from the third wind box 32 c into thefluidized bed 14, while keeping the flow rate of this fluidizing gas.Further, when low-temperature abnormality occurs in the second regionua₂ of the fluidized bed 14, the control section 50 controls the feedingunit 33 to open the valve 37 c and close the valve 38 c to increase theair ratio of the fluidizing gas to be blown from the third wind box 32 cinto the fluidized bed 14, while keeping the flow rate of thisfluidizing gas.

Further, the control section 50 operates to monitor a local temperatureabnormality of the fluidized bed 14 caused when fluidization abnormalityof the fluidized bed 14 (local defective fluidization, etc., in thefluidized bed 14) occurs. Then, when temperature abnormality isdetected, the control section 50 controls the feeding unit 33 to adjustthe air ratio and/or the flow rate of the fluidizing gas to be fed toeach of the wind boxes 32, thereby solving the fluidization abnormalityof the fluidized bed 14.

Specifically, in a specific region of the fluidized bed 14 wheredefective fluidization occurs, the fluidizable particles 12 are notsufficiently agitated because flowability (mobility) of the fluidizinggas in the specific region is different from the remaining region. Thiscauses a temperature difference between an upper side and a lower sideof the specific region. Therefore, the control section 50 operates todetect a temperature difference in the specific region to detect localdefective fluidization in the fluidized bed 14, i.e., fluidizationabnormality of the fluidized bed 14. Upon detection of the defectivefluidization (the fluidization abnormality), the control section 50operates to adjust the flow rate of the fluidizing gas to be supplied tothe inside of the furnace body 20.

More specifically, the control section 50 is configured to control anup-down directional (vertical) temperature in each of the regions of thefluidized bed 14, in the following manner.

In response to receiving temperature signals from the temperaturesensors 40, the control section 50 acquires temperatures in each of theregions (regions in which the temperature sensors 40 are allocated) ofthe fluidized bed 14. The control section 50 calculates a temperaturedifference (ΔT₁(=T₁−T₄), ΔT₂(=T₂−T₅), ΔT₃(=T₃−T₆)) between the upperposition and the lower position in each of the regions of the fluidizedbed 14. Then, the control section 50 compares each of the temperaturedifferences ΔT₁, ΔT₂, ΔT₃ with a predetermined given value to performmonitoring (detection) on whether the local defective fluidization inthe fluidized bed 14 occurs. This monitoring may be performedcontinually or may be performed at intervals of a given time.

For example, in the case where the given value is set to ±10° C., whenthe relation “ΔT₁, ΔT₂ or ΔT₃>10° C.” or “ΔT₁, ΔT₂ or ΔT₃<−10° C.” issatisfied, the control section 50 operates to temporarily increase aflow rate of the fluidizing gas to be supplied to the correspondingregion. Specifically, when the relation “ΔT₁<−10° C.” is satisfied, thecontrol section 50 controls the feeding section 33 to temporarilyincrease a flow rate of the fluidizing gas to be blown from the firstwind box 32 a into the fluidized bed 14, from a normal flow rate (e.g.,Uo/Umf=3.0) (for example, an increased flow rate Uo/Umf=5.0). In thisprocess, the control section 50 operates to increase only the flow ratewithout changing an air ratio of the fluidizing gas. Then, when therelations “ΔT₁>−10° C.” and “ΔT₁<10° C.” are satisfied, the controlsection 50 controls the feeding unit 33 to return the flow rate of thefluidizing gas to be blown from the first wind box 32 a into thefluidized bed 14, to an original value (e.g., return the Uo/Umf from 5.0to 3.0), and continues the temperature monitoring. On the other hand, ina situation where the relation “ΔT₁<−10° C.” is still satisfied evenwhen a certain time has elapsed after starting to increase the flowrate, the control section 50 determines that abnormality occurs in theinside of the furnace body 20 and stops the operation of the fluidizedbed furnace 10.

Furthermore, the control section 50 is configured to perform control ofthe waste supply section 60, etc.

The waste supply section 60 is designed to supply waste 18 from thefront wall 24 to a region on the fluidized bed 14 adjacent to the frontwall 24. The waste supply section 60 in this embodiment is a screwextruder. The screw extruder is capable of continuously supply waste 18to the inside of the furnace while guaranteeing sealing performance. Thescrew extruder is also capable of supplying trash which is likely to bescattered due to its small bulk specific gravity, such as paper orplastic sheet, to the inside of the furnace body 20 while keeping amassive form. This makes it possible to suppress scattering of trashinside the furnace body 20, as compared to a conventional furnace inwhich trash is input from an upper portion thereof. It is to beunderstood that the configuration of the waste supply section 60 is notlimited to a specific type. For example, although the waste supplysection 60 in this embodiment is configured to push waste 18 into thefurnace by using the screw extruder, it may be configured to push waste18 into the furnace by using a pusher or the like.

In the fluidized bed furnace 10 configured as above, a combustible gasis recaptured from waste 18 in the following manner.

At the start of the operation of the fluidized bed furnace, the controlsection 50 operates to cause the fluidizing gas from each of the windboxes 32 toward the fluidizable particles 12 supported by the bottomwall 21 inside the furnace body 20. At the start of the operation, thereis not any waste 18 on the fluidized bed 14 (if any, an amount thereofis very small), so that the control section 50 instructs anon-illustrated burner or the like to heat the fluidizable particles 12as a bed material from above the fluidized bed 14. In this process, thecontrol section 50 operates to fluidize the fluidizable particles 12 bysupplying only air from each of the wind boxes 32 to the fluidizableparticles 12 without blowing steam, and heat the fluidizable particles12 in the fluidized state. Then, when the entire fluidized bed 14 isheated to a given temperature (e.g., 600° C.), the control section 50instructs the waste supply section 60 to start to input waste 18 intothe furnace body 20. In this process, the control section 50 operates togradually suppress an operation of the burner or the like, and reduce anamount of supply of air, while increasing an amount of addition ofsteam, to set a ratio therebetween to a given value.

The air ratio of the fluidizing gas to be blown from each of the windboxes 32 toward the fluidizable particles 12 is preliminarily derived asa value suitable for operation of the fluidized bed furnace, and storedin the control section 50. In other words, as long as no temperatureabnormality occurs in the fluidized bed 14 during the operation of thefluidized bed furnace 10, the control section 50 operates to supply agiven amount of air and a given amount of steam to each of the windboxes 32 without adjusting the valve openings of the valves 37 a, 37 b,37 c, 38 a, 38 b, 38 c.

The fluidizable particles 12 are set in the fluidized state in the abovemanner, so that the fluidized bed 14 is formed inside the furnace body20. In this state, while respective fluidizing gases to be blown fromthe wind boxes 32 into the fluidized bed 14 are identical in flow rate,they are different from each other in terms of air ratio. Specifically,the control section 50 operates to adjust the valve openings of thevalves 37 a, 37 b, 37 c, 38 a, 38 b, 38 c to allow an air ratio of thefluidizing gas to be fed to the second wind box 32 b to become largerthan an air ratio of the fluidizing gas to be fed to the first wind box32 a, and allow an air ratio of the fluidizing gas to be fed to thethird wind box 32 c to become larger than an air ratio of the fluidizinggas to be fed to the second wind box 32 b, so as to cause thetemperature of the fluidized bed 14 to be raised in the direction fromthe front wall 24 toward the rear wall 25.

As above, the control section 50 operates to change the oxygenconcentration in each of the regions in the fluidized bed 14 to therebyform a given temperature distribution (i.e., a temperature distributionin which the temperature of the fluidized bed 14 is raised in thedirection from the front wall 24 toward the rear wall 25), while settingthe flow rate of the fluidizing gas to be blown from each of the windboxes 32 into the fluidized bed 14, to a constant value, to therebydesirably maintain the fluidized state in each of the regions in thefluidized bed 14.

When Ave1, Ave2 and Ave3 become about 600° C., about 650° C. and about700° C., respectively, the control section 50 determines that the insideof the furnace is set in a steady state, and starts temperature control.In this embodiment, the control section 50 is configured to perform thetemperature control of the fluidized bed 14 to allow a temperaturedifference between Ave1 and Ave3 to become equal to or greater than 50°C., and allow Ave1 and Ave3 to fall with the range of 600 to 700° C. andthe range of 700 to 800° C., respectively.

Specifically, the screw extruder (the waste supply section 60) pusheswaste 18 generally horizontally toward the inside of the furnace body20. Through this operation, the waste 18 is pushed onto the first regionua₁ (see FIGS. 1 and 2). The active fluidized bed 14 is formed insidethe furnace body 20. Thus, the input waste 18 is moved from the frontwall 24 toward the rear wall 25 while being entrapped by the fluidizedbed 14 and spread by a spreading action of the fluidized bed 14. Infact, instead of being moved in only one direction from the front wall24 toward the rear wall 25, the waste 18 in the fluidized bed 14 ismoved from a region having the waste 18 at a relatively high density toa region having the waste 18 a at a relatively low density (i.e., fromthe input side (front wall 24) toward the rear wall 25) in a graduallyspreading manner, while repeating reciprocating movements in theup-down, right-left and front-rear directions.

The first region ua₁ of the fluidized bed 14 has a desirably lowtemperature. Thus, in the above process, rapid combustion of the waste18 is suppressed, and easily gasifiable substances in the waste 18 aregasified. In other words, easily gasifiable waste 18 such as plastic orpaper is gasified in the first region ua₁ and a region adjacent thereto.On the other hand, not-easily gasifiable waste such as a wood piece ispartially gasified, but a large part thereof is gradually moved towardthe rear wall 25 according to fluidization of the fluidizable particles,etc., and will reach the second region ua₂ without being gasified. Inthis manner, the easily gasifiable waste 18 is gasified under a mildcondition (low temperature) in the first region ua₁ or the adjacentregion (on the side of the second region ua₂) before it reaches thesecond region ua₂, so that it becomes possible to suppress a fluctuationof generation of a combustible gas.

Then, the moved waste 18 is sufficiently mixed with the fluidizableparticles 12 in a region of the fluidized bed 14 vertically overlappingwith the discharge port 29, and a high-temperature region therearound,so that uncombusted waste 18 remaining after passing through the regionon the side of the front wall 24 is sufficiently gasified.

As above, according to the screw extruder 60, waste 18 is continuouslysupplied to the fluidized bed 14 having a temperature distribution inwhich the temperature of the fluidized bed 14 is raised in the directionfrom the front wall 24 toward the rear wall 25, so that it becomespossible to suppress intermittent and rapid generation of a combustiblegas. Consequently, the generation of a combustible gas is stabilized.

The fluidizable particles 12 discharged from the fluidized bed 14through the discharge port 29 together with non-combustible substancesand others are input into the furnace body 20 again, according to need.

In a situation where abnormality in the temperature distribution of thefluidized bed 14 occurs (i.e., a region having an excessively low orhigh temperature locally occurs), or fluidization abnormality (i.e.,local defective fluidization in the fluidized bed 14, etc.) occurs, dueto an amount of input of waste 18, a composition of trash comprised inwaste 18, etc., the control section 50 is operable, based on thetemperatures detected by the temperature sensors 40, to control the gasfeeding section 30 to adjust the flow rate of air and/or the flow rateof steam to be fed to each of the wind boxes 32, as mentioned above. Inthis way, the control section 50 can solve the temperature distributionabnormality and fluidization abnormality in the fluidized bed 14.

A combustible gas generated inside the furnace body 20 is supplied fromthe combustible gas outlet portion 23 to a subsequent stage such as agas engine for electric power generation processes, via a duct or thelike connected to the combustible gas outlet portion 23. In thisprocess, steam included in the combustible gas is condensed into waterdue to a lowering in temperature of the combustible gas, and the wateris collected. Thus, a combustible gas after removal of steam will besupplied to the subsequent stage of the fluidized bed furnace 10.

As mentioned above, in the fluidized bed furnace 10 according to theabove embodiment, waste 18 is supplied from the waste supply section 60to the side of the first region ua₁ of the fluidized bed 14 whosetemperature is raised in the direction from the first region ua₁ towardthe second region ua₂, so that it becomes possible to suppress a rapidfluctuation in amount, concentration, etc., of a generated combustiblegas. As a result, a combustible gas is stably generated from waste 18.

Specifically, waste 18 is supplied to the side of the first region ua₁of the fluidized bed 14 having a desirably low temperature, so that itbecomes possible to suppress rapid combustion of easily combustibletrash in the waste 18. In addition, an amount of generation of acombustible gas based on gasification of the waste 18 is small. Thiswaste 18 is moved inside the furnace body 20 toward the discharge port29 (i.e., toward the second region ua₂ of the fluidized bed 14),according to fluidization of the fluidizable particles 12 making up thefluidized bed 14 and supply of new waste 18 into the furnace body 20 bythe waste supply section 60. The second region ua₂ has a desirably hightemperature, so that the waste 18 moved from the side of the firstregion ua₁ is sufficiently gasified in the second region ua₂ to generatea combustible gas. This makes it possible to suppress intermittent andrapid generation of a combustible gas, and stabilize the generation ofthe combustible gas.

In the above embodiment, respective air ratios of the fluidizing gasesto be supplied to the regions of the fluidized bed 14 are adjusted inthe direction from the front wall 24 toward the rear wall 25 (or thedischarge port 29) to adjust respective temperatures of the regions ofthe fluidized bed 14. Thus, the fluidization abnormality (localdefective fluidization in the fluidized bed 14, etc.) becomes lesslikely to occur in the fluidized bed 14. In other words, it becomespossible to adjust the air ratio (i.e., oxygen concentration) of thefluidizing gas to be supplied to fluidized bed 14 to thereby adjust thetemperature in each of the regions of the fluidized bed 14, whilesufficiently ensuring the flow rate of the fluidizing gas to be suppliedto each of the regions of the fluidized bed 14 to thereby desirablymaintain the fluidized state of the fluidizable particles 12 in each ofthe regions of the fluidized bed 14. In addition, respectivetemperatures of the upper and lower positions vertically spaced in eachof the first region ua₁, the second region ua₂ and the third region ua₃are detected, so that, if defective fluidization occurs in one of theregions, the defective fluidization can be reliably detected.

In the above embodiment, the upper surface 21 a of the bottom wall 21 ofthe furnace body 20 is inclined to become lower toward the dischargeport, so that non-combustible substances, carbides and others sinkingdown to the bottom wall 21 in the fluidized bed 14 fall on the uppersurface 21 a of the bottom wall 21 toward the discharge port 29. Thus,the non-combustible substances and others can be easily discharged fromthe furnace body 20.

It is to be understood that a fluidized bed furnace of the presentinvention are not limited to the above embodiment, but various changesand modifications may be made therein without departing from the spiritand scope of the present invention hereinafter defined.

In addition to the positions for detecting the temperatures of the upperand lower positions, the temperature sensors 40 to be allocated in theupside regions ua₁, ua₂, ua₃ may be additionally disposed at a positionfor detecting a temperature of an intermediate position between theupper and lower positions.

In the above embodiment, the temperature sensors 40 are arrangedside-by-side at intervals and at the same height, in the front-reardirection. Alternatively, the temperature sensors 40 may be arranged atdifferent heights in respective ones of the upside regions ua₁, ua₂,ua₃.

In the case where each of two wind boxes on both front and rear sides ofthe discharge port 29 (in FIG. 3, left and right sides of the dischargeport 29) are located adjacent to the discharge port 29, the wind boxclosest to the discharge port 29 means the two wind boxes . However, inview of desirable temperature control of the entire fluidized bed 14, itis preferable to control the upside region corresponding to one of thewind boxes on a rear (in FIG. 3, right) side of the discharge port 29.

Outline of Embodiment

The outline of the above embodiment is as follows.

The fluidized bed furnace according to the above embodiment is designedto heat waste to extract a combustible gas from the waste. The fluidizedbed furnace comprises: a furnace body having a bottom wall whichsupports fluidizable particles from therebelow so as to make up afluidized bed for heating the waste, and a sidewall standing upwardlyfrom the bottom wall, wherein the bottom wall has a discharge portprovided at a position offset from a center position of the bottom wallin a specific direction to discharge non-combustible substances in thewaste together with a part of the fluidizable particles, and an uppersurface of the bottom wall is inclined to become lower toward thedischarge port so as to cause the non-combustible substances to fall onthe upper surface of the bottom wall toward the discharge port; a gassupply section for blowing a fluidizing gas from the bottom wall of thefurnace body toward the fluidizable particles to fluidize thefluidizable particles; a plurality of temperature detection sections fordetecting a temperature of the fluidized bed; a control section forcontrolling the gas supply section; and a waste supply section forsupplying waste from a supply-side portion of the sidewall located on aside opposite to the discharge port across the center position of thebottom wall, to a region on the fluidized bed, the region being adjacentto the supply-side sidewall portion. The gas supply section includes aplurality of wind boxes each of which is provided on a lower side of thebottom wall to extend in a direction orthogonal to a direction from thesupply-side sidewall portion toward the discharge port and adapted toblow the fluidizing gas from a given position in the orthogonaldirection toward the fluidizable particles, and a feeding unit adaptedto feed the fluidizing gas to each of the wind boxes in a manner capableof adjusting an air ratio of the fluidizing gas to be fed to each of thewind boxes, individually. The plurality of wind boxes are arrangedside-by-side in the direction from the supply-side sidewall portiontoward the discharge port. The plurality of temperature detectionsections are disposed at respective positions allowing detection oftemperatures of an upper position and a lower position which arevertically spaced in a first region of the fluidized bed verticallyoverlapping with a first one of the wind boxes closest to thesupply-side sidewall portion, and allowing detection of temperatures ofan upper position and a lower position which are vertically spaced in asecond region of the fluidized bed vertically overlapping with thedischarge port or a second one of the wind boxes closest to thedischarge port. The control section is operable, based on thetemperatures detected by the temperature detection sections, to adjustan air ratio of the fluidizing gas to be fed from the feeding unit toeach of the wind boxes, individually, in such a manner that thetemperature of the fluidized bed is raised in a direction from the firstregion toward the second region.

In the present invention, waste is supplied from the waste supplysection to the side of the first region of the fluidized bed whosetemperature is raised in a direction from the first region toward thesecond region, so that it becomes possible to suppress a rapidfluctuation in amount, concentration, etc., of a generated combustiblegas. As a result, a combustible gas is stably generated from waste.

Specifically, waste is supplied to the side of the first region of thefluidized bed having a desirably low temperature, so that it becomespossible to suppress rapid combustion of easily combustible trash in thewaste. In addition, an amount of generation of a combustible gas basedon gasification of the waste is small. This waste is moved inside thefurnace body toward the discharge port (i.e., toward the second regionof the fluidized bed), according to fluidization of the fluidizableparticles making up the fluidized bed and supply of new waste into thefurnace body by the waste supply section. The second region has adesirably high temperature, so that the waste moved from the side of thefirst region is sufficiently gasified in the second region to generate acombustible gas. This makes it possible to suppress intermittent andrapid generation of a combustible gas, and stabilize the generation ofthe combustible gas.

Further, respective air ratios of the fluidizing gases to be supplied tothe regions of the fluidized bed are adjusted in the direction from thesupply-side sidewall portion toward the discharge port to adjustrespective temperatures of the regions of the fluidized bed, so thatfluidization abnormality becomes less likely to occur in the fluidizedbed. In other words, it becomes possible to adjust the air ratio (i.e.,oxygen concentration) of the fluidizing gas to be supplied to fluidizedbed to thereby adjust a temperature in each of the regions of thefluidized bed, while sufficiently ensuring a flow rate of the fluidizinggas to be supplied to each of the regions of the fluidized bed tothereby desirably maintain a fluidized state of the fluidizableparticles in each of the regions of the fluidized bed.

In addition, respective temperatures of the upper and lower positionsvertically spaced in each of the first region and the second region aredetected, so that, if defective fluidization occurs in one of theregions, the defective fluidization can be reliably detected.Specifically, in a situation where, when the fluidizing gas is suppliedfrom the bottom wall into the fluidized bed, the fluidizable particlesin a region supplied with the fluidizing gas is in a sufficientlyfluidized state, the supplied fluidizing gas will easily move upwardlythrough the fluidized bed. However, if defective fluidization occurs inthe region, the fluidizing gas becomes hard to move upwardly through thefluidized bed. Thus, in the region having the defective fluidization,the fluidizable particles are not sufficiently agitated, which causes atemperature difference between the upper and lower positions. Thistemperature difference is detected to detect the defective fluidization.

Further, the upper surface of the bottom wall of the furnace body isinclined to become lower toward the discharge port, so thatnon-combustible substances sinking down to the bottom wall in thefluidized bed fall on the upper surface of the bottom wall toward thedischarge port. Thus, the non-combustible substances can be easilydischarged from the furnace body.

In the fluidized bed furnace according to the above embodiment, specificones of the plurality of temperature detection sections are allocatedbetween the first region and the second region of the fluidized bed, andwherein the specific temperature detection sections are disposed atrespective positions allowing detection of temperatures at givenintervals in the direction from the supply-side sidewall portion towardthe discharge port.

According to this feature, temperatures between the first region and thesecond region can be detected, so that, if temperature abnormality suchas local lowering in temperature occurs between the first and secondregions, the abnormality can be detected. This makes it possible to copewith the local temperature abnormality.

In this case, preferably, the specific temperature detection sectionsallocated between the first region and the second region are disposed atrespective positions allowing detection of temperatures in each of oneor more regions of the fluidized bed vertically overlapping withrespective ones of the remaining one or more wind boxes disposed betweenthe first wind box and the second wind box.

According to this feature, temperatures in a region of the fluidized bedthrough which the fluidizing gas supplied from each of the wind boxespasses are detected, so that it becomes possible to facilitateadjustment of the air ratio of the fluidizing gas to be fed to each ofthe wind boxes.

Further, in each of the one or more regions between the first region andthe second region, and at a position vertically overlapping withrespective ones of the remaining one or more wind boxes, the specifictemperature detection sections are disposed at respective positionsadditionally allowing detection of temperatures of an upper position anda lower position which are vertically spaced.

According to this feature, defective fluidization in each region rangingfrom the first and second regions in the fluidized bed can be desirablydetected.

INDUSTRIAL APPLICABILITY

As above, the fluidized bed furnace of the present invention is usefulfor heating waste in a fluidized bed formed by fluidizing fluidizableparticles, to extract a combustible gas from the waste, and suited tostably obtain a combustible gas even from waste comprising easilycombustible trash.

What is claimed is:
 1. A fluidized bed furnace for heating waste toextract a combustible gas from the waste, comprising: a furnace bodyhaving a bottom wall which supports fluidizable particles fromtherebelow so as to make up a fluidized bed for heating the waste, and asidewall standing upwardly from the bottom wall, wherein the bottom wallhas a discharge port provided at a position offset from a centerposition of the bottom wall in a specific direction to dischargenon-combustible substances in the waste together with a part of thefluidizable particles, and an upper surface of the bottom wall isinclined to become lower toward the discharge port so as to cause thenon-combustible substances to fall on the upper surface of the bottomwall toward the discharge port; a gas supply section for blowing afluidizing gas from the bottom wall of the furnace body toward thefluidizable particles to fluidize the fluidizable particles; a pluralityof temperature detection sections for detecting a temperature of thefluidized bed; a control section for controlling the gas supply section;and a waste supply section for supplying waste from a supply-sideportion of the sidewall located on a side opposite to the discharge portacross the center position of the bottom wall, to a region on thefluidized bed, the region being adjacent to the supply-side sidewallportion, wherein: the gas supply section includes a plurality of windboxes each of which is provided on a lower side of the bottom wall toextend in a direction orthogonal to a direction from the supply-sidesidewall portion toward the discharge port and adapted to blow thefluidizing gas from a given position in the orthogonal direction towardthe fluidizable particles, and a feeding unit adapted to feed thefluidizing gas to each of the wind boxes in a manner capable ofadjusting an air ratio of the fluidizing gas to be fed to each of thewind boxes, individually, wherein the plurality of wind boxes arearranged side-by-side in the direction from the supply-side sidewallportion toward the discharge port; the plurality of temperaturedetection sections are arranged at respective positions allowingdetection of temperatures of an upper position and a lower positionwhich are vertically spaced in a first region of the fluidized bed, thefirst region being vertically overlapping with a first one of the windboxes closest to the supply-side sidewall portion, and allowingdetection of temperatures of an upper position and a lower positionwhich are vertically spaced in a second region of the fluidized bed, thesecond region being vertically overlapping with the discharge port or asecond one of the wind boxes closest to the discharge port; and thecontrol section is operable to adjust an air ratio of the fluidizing gasto be fed from the feeding unit to each of the wind boxes, individually,based on the temperatures detected by the temperature detectionsections, so as to make the temperature of the fluidized bed be raisedin a direction from the first region toward the second region.
 2. Thefluidized bed furnace as defined in claim 1, wherein specific ones ofthe plurality of temperature detection sections are allocated betweenthe first region and the second region of the fluidized bed, and whereinthe specific temperature detection sections are arranged so as to becapable of detecting of temperatures at respective positions at givenintervals in the direction from the supply-side sidewall portion towardthe discharge port.
 3. The fluidized bed furnace as defined in claim 2,wherein the specific temperature detection sections allocated betweenthe first region and the second region are arranged so as to be capableof detecting of temperatures at respective positions in each of one ormore regions of the fluidized bed, the regions being verticallyoverlapping with respective ones of the remaining one or more wind boxesdisposed between the first wind box and the second wind box.
 4. Thefluidized bed furnace as defined in claim 3, wherein, in each of the oneor more regions between the first region and the second region, and at aposition vertically overlapping with respective ones of the remainingone or more wind boxes, the specific temperature detection sections arearranged so as to be capable of detecting of temperatures at respectivepositions of an upper position and a lower position which are verticallyspaced.